1. Field of the Invention
This invention relates to neutron detectors. More specifically, it refers to a neutron detector capable of measuring neutron radiation wherein at least two photodetectors are employed, spaced apart by a gap between them wherein a substance is disposed which permits scintillation in the absorption of neutron radiation thereby permitting the detector to differentiate neutron radiation from gamma radiation.
2. Description of the Prior Art
Neutron detectors are known in the prior art. Real time personal neutron detectors are required, to name a few examples, for occupational radiation protection at nuclear power plants, nuclear material processing facilities, high-energy particle accelerators, high altitude flights and long-term space missions. In addition, there is a need for detection of neutron radiation at oil well sites, for on-site nuclear monitoring and for dosimetry at nuclear facilities.
One recently discussed neutron detector technique uses a silicone PIN photodiode with a gadolinium-foil converter. The converter emits a number of conversion electrons with energies between 29 and 246 kev and gamma-rays in the range of >231 keV energies per a single neutron capture. The method needs simultaneous measurements of electrons and gamma rays and subtraction of the effect from gamma-interactions. That makes the technique complicated and sensitive to calibration procedure. The gadolinium foil must be thinner than 25 microns to allow electrons to effectively escape from the foil. With 1 cm2 sensitive area, the detector has an efficiency of 5.6% at ideal conditions.
There is another method of measuring thermal neutron fluxes for nuclear monitoring purposes with gas proportional counters but these detectors are sensitive to gamma ray background and have relatively low efficiency in pocket-size configurations. In these detectors, the gas (3He or BF3) is limited in pressure by a few atmospheres because of low electron-ion yield from tracks of decay protons or alpha-particles and technical limitations in the application of sufficiently high voltage for effective charge application in the pressurized gases.
U.S. Pat. No. 3,102,198 describes thermal neutron detectors employing 3He gas under pressure in a neutron pervious sealed container. A low voltage power supply is connected by way of a conductor and resistor to a center electrode in the sealed container. This detector is undesirably bulky and sensitive to gamma ray background.
A need exists for an improved detector with high detection efficiency to neutrons of different energies yet having low sensitivity to gamma-ray background.